Population structure, speciation and reticulated evolution in the hydrothermal vent environments of the eastern Pacific and mid Atlantic

Vent communities are typically restricted to small, isolated patches of habitat. Vent habitats, however, are found throughout the world, and new biogeographic provinces are still being described. Six vent biogeographic provinces, defined by species assemblages, are currently recognized. Vicariance (i.e., geographic isolation of taxa usually associated with a geological boundary) is hypothesized to have contributed to the formation of several of these provinces. Vicariance also occurs within biogeographic provinces. Whether on time scales associated with taxonomic divergence in community assemblages (e.g., the formation of biogeographic provinces: 10's of millions of years), or on time scales associated the formation of species (e.g., hundreds of thousands to a few million years), understanding both the extrinsic forces that contribute to speciation in these environments (e.g., geologic processes or physical oceanography) and the intrinsic forces that maintain species after formation (pre- and postzygotic barriers to reproduction) contribute to our understanding of the creation and maintenance of biodiversity in these habitats. Chapter two addresses the role that extrinsic forces have played in limiting dispersal in a hydrothermal vent tubeworm, Ridgeia piscesae, found in the northeast Pacific. R. piscesae 's range encompasses two transform faults that we hypothesize might restrict larval dispersal. We test this hypothesis examining both mitochondrial and allozyme data. We also compare the directionality of gene flow and model-based estimates of bathymetrically induced circulation in this region to evaluate whether these models might be useful in predicting regions of restricted dispersal as previously suggested. A recently discovered hybrid population of bathymodiolid mussels on the Mid-Atlantic ridge motivated chapters three and four. In chapter three, we develop a Bayesian test of cytonuclear disequilibrium in genetic data. We apply this new methodology to the hybrid population of bathymodiolid mussels and find significant cytonuclear disequilibrium. Chapter four develops a Bayesian estimator of immigration proportions and proposes a test of model adequacy under this model. These two chapters advance genetic analyses of hybrid populations and contribute to our understanding of the intrinsic factors that maintain species upon secondary contact.